This is a nice comment. Would it not be easier to work with ARRs from
the beginning? Is NNT really simpler to transmit to clinicians as ARR? I
doubt it.
Rolf
W Y Zhang schrieb:
>
> Yes, there is a way to make NNT and its CIs symmetric, that is to
> convert the values back to their originals, ie., absolute risk
> difference (ARR). Douglas Altman (BMJ 1998;317:1309-1312) suggested
> to present NNT and CIs by relabelling ARR scale. From there you can
> see a symmetric graph but asymmetric label just like log value
> conversion.
>
> Weiya
>
> > When calculating the NNT for a treatment that is barely statistically
> > significant and has a large NNT, the confidence interval is wide and very
> > asymmetrical. For example in women with prior vertebral fractures and
> > femoral neck BMD at least 2.1 standard deviations below young normal, the
> > NNT with alendronate for 3 years to prevent one hip fracture =91 (95% CI
> > 59-4545)
> >
> > I assume that if I were to able to calculate a mean NNT, it would be higher
> > than 91, perhaps 200-300. Is their a formula for recalulating the NNT to
> > adjust for this asymmetry? and is this a reasonable thing to do?
> >
> > Thanks
> > Mick Braddick
> > Clinical Epidemiologist
> > Group Health Cooperative
> > Seattle
> > USA
> >
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Prof. Dr. Rolf R. Engel ([log in to unmask])
Psychiatric Hospital, University of Munich
Nussbaumstr. 7, D-80336 München
Tel ..49 89 51605561, Fax ..49 89 51605562
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